Driveline power transmitting devices such as gears or transmissions, especially axle fluids and manual transmission fluids (MTFs), present highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating requirements, whilst providing durability and fuel economy. One of the important parameters influencing performance is lubricant viscosity. It is known that lubricants capable of performing at lower viscosity typically provide increased fuel economy. Conversely, lower viscosity fluids also contribute to elevated gear and transmission operating temperatures, especially for higher torque applications. Additionally, increasing lubricant viscosity is believed to provide better wear protection and durability to gears and transmissions. Consequently, it would be desirable to provide a correctly balanced lubricant composition to meet the needs of gears and transmissions.
U.S. Pat. No. 6,251,840 discloses a lubrication fluid for reduced air entrainment and improved gear protection. The lubrication fluid contains 0.025 wt % to 5 wt % of a 2,5-dimercapto-1,3,4-thiadiazole derivative. In one embodiment the 2,5-dimercapto-1,3,4-thiadiazole derivative discloses a DMTD/succinimide. The DMTD/succinimide may be prepared by the procedure of U.S. Pat. No. 4,136,043.
U.S. Pat. No. 4,136,043 discloses DMTD/succinimide dispersants and their methods of preparation. The dispersants formed contain 0.1-10 parts by weight of succinimide per part of DMTD. In the example section all of the DMTD/succinimide dispersants are prepared from succinic anhydride using chlorine.
EP 1 308 496 A2 discloses lubricating oils containing hydrocarbyl esters of a phosphorous acid and compounds with a 5-membered ring and at least two double bonded nitrogen atoms.